The present invention concerns a novel hydroformylation process for olefinically unsaturated compounds using carbon monoxide and hydrogen, in which the catalytic system is a solution of at least one transition metal compound in a non-aqueous organic-inorganic ionic salt which is liquid at the reaction temperature, and in which the products of the hydroformylation reaction are slightly soluble or insoluble.
Hydroformylation of olefinic compounds is a reaction which is industrially very important. The majority of processes use catalysts which are dissolved in an organic phase constituted by the reactants, products and possibly excess ligands, even though there are difficulties in separating and recovering the catalyst, in particular when the latter is a noble metal such as rhodium.
One mode of resolving this problem has been described in French patent FR-A-2 314 910. It consists of carrying out hydroformylation in the presence of an aqueous solution containing a rhodium complex which is rendered water-soluble by the presence of a sulphonated phosphine ligand which is itself water-soluble, such as the sodium salt of trisulphonated triphenylphosphine. In this way, the organic phase containing the aldehydes is readily separated from the aqueous phase containing the catalyst. This technique has formed the subject matter of a considerable number of studies which were discussed in an article by W. A. Hermann in "Angewandte Chemie International" in 1993, volume 32, page 1524 ff. Despite the great industrial importance of this technique for propylene hydroformylation, such a two-phase system suffers from a lack of solubility in water of the olefins, leading to relatively low reaction rates which renders it inapplicable to long chain olefins.
United States patent US-A-3 565 823 describes a technique consisting of dispersing a transition metal compound in a salt of tin or germanium and a quaternary ammonium or phosphonium with formula (R.sub.1 R.sub.2 R.sub.3 R.sub.4 Z)YX.sub.3 where R.sub.1, R.sub.2, R.sub.3, R.sub.4 are hydrocarbyl residues containing up to 18 carbon atoms, Z is nitrogen or phosphorous, Y is tin or germanium and X is a halogen, chlorine or bromine, the non-aqueous medium with ionic nature constituting a "molten salt". US-A-3 657 368 describes a process for hydrogenating olefins and US-A-3 919 271 describes a process for hydrogenating nitrites each using the above tin and germanium based composition. US-A-3 832 391 claims an olefin carbonylation process using the same composition.
European patent application EP-A-0 107 430 describes a hydroformylation process using a ruthenium catalyst dispersed in a quaternary phosphonium or ammonium salt or base with a melting point which is lower than the reaction temperature.
The anions of the salt used are the halides, nitrate, acetate, chromate or hydroxide. Tetrabutylphosphonium tetrafluoroborate can also be used.
All those salts have melting points of at least 100.degree. C., more generally at least 120.degree. C. The solid ruthenium catalyst is mixed with the solid salt and, in the presence of the reactant, is heated in its entirety to the reaction temperature at which the medium is liquid. The compositions described above have the disadvantage of having a relatively high melting point, the hydroformylation reaction thus being carried out at at least 90.degree. C., or generally 160.degree.-180.degree. C. in EP-A-0 107 430.